Field of the Invention
The present invention relates to a structure of an electronic apparatus provided with a metal core substrate mounting electronic parts thereon, and a manufacturing technique thereof.
It is necessary that the electronic apparatus provided with the electronic substrate is structured such as to generate no defect caused by a heat generation by the electronic parts. Accordingly, a heat cycle test is executed before shipping. In particular, in an electronic part for vehicle used such as an ECU or the like, it is affected by whether or not an LSI chip generates heat due to an engine on or off in addition to a temperature change within a vehicle body in accordance with a change of environment or the like, and it is necessary that the electronic part or the like stands against a thermal cycle (for example, xe2x88x9240 degrees to 120 degrees: environmental test general rule JAS0D001 of electronic device for motor vehicle) in a wide temperature range. In recent years, there is a tendency that the ECU is arranged close to the engine, that is, there is a tendency that an upper limit of the temperature range becomes higher. When being exposed to the thermal cycle mentioned above a performance of the electronic parts within the ECU becomes unstable, and a connection defect between the mounting substrate for the electronic parts and the electronic parts tends to be generated. That is, a high heat radiating performance is required in the electronic apparatus, and more particularly, a heat radiating performance which is more excellent than that of the general electronic part is required in the electronic part for vehicle use such as the ECU or the like.
A prior art relating to a structure of a general electronic apparatus taking into consideration heat generation of the electronic part mounted on the substrate includes JP-A-6-169189.
In this publication, there is described an electronic circuit board in which a pad for a heat radiating electrode connected to a ground via a through hole is formed on a printed circuit board having the ground in an inner layer, and the pad for the heat radiating electrode and the heat radiating electrode provided in a chip type heat generating part are mounted so as to align. The structure of the electronic circuit board secures a heat radiating performance of the printed circuit board by radiating a heat generated by the chip type heat generating part to the ground via the heat radiating electrode, the pad for the heat radiating electrode and the through hole.
Further, there is a metal core substrate as a substrate for general electronic parts, and there is JP-A-7-326690 as a prior art taking into consideration a heat radiating performance of the metal core substrate.
In this publication, there is described a matter that an internal wiring pattern is formed on the metal core substrate, an outer lead is connected to the internal wiring pattern, the internal wiring pattern is formed by processing a thin film, for example, etching a copper film or the like, and a portion on which a chip part of the metal core substrate on which the internal wiring pattern is formed is mounted is formed in a recess portion.
JP-A-6-169189 describes neither a heat radiating structure corresponding to a kind of a substrate nor a metal core substrate since a glass epoxy material is used as a core of the substrate. Further, since a ground terminal of a semiconductor part is also set to a fixed size in the same manner as the other signal terminals, it is not sufficient to secure a heat radiating performance.
Further, in JP-A-7-326690, since a metal core substrate is used, a heat diffusion efficiency of the substrate itself is improved, however, since an organic adhesive agent such as an epoxy resin or the like or an organic insulating layer such as a polyimide or the like is provided between the metal core substrate and the electronic part, a heat conductivity from the electronic part to the substrate is low. That is, it is not said that the heat conductivity from the electronic part to the mounting substrate is sufficiency considered.
Further, no consideration is given to a connection defect between a semiconductor part terminal and a wiring which is generated in the case of forming the wiring on the metal core substrate in accordance with the prior art and employing a flip chip type semiconductor part in the wired metal core substrate.
Further, no consideration is given to a heat radiating structure in the case of mounting an electronic substrate to the other substrate as an interposer or the case of a multi chip module (MCM) in which a plurality of chips are mounted.
An object of the present invention is to improve a heat radiating performance of an electronic substrate by using a structure of a metal core substrate and to improve a heat radiating performance (heat resistance) of a whole of the electronic parts.
Further, another object of the present invention is to improve a heat radiating performance (heat resistance) of a whole of electronic parts having a substrate mounting an interposer thereon and a substrate employing the MCM structure.
One of the aspects in accordance with the present invention includes an electronic apparatus comprising:
a metal core substrate provided with a core member constituted by a metal plate or a complex metal plate and a wiring layer formed on the core member; and
an electronic part having a terminal connected to the wiring layer,
wherein a high heat conducting member is arranged so that the core member and the electronic part are adjacent to each other via the high heat conducting member.
In accordance with the structure mentioned above, a heat radiating performance of the electronic apparatus is improved.
Further, in the case of using the substrate mentioned above for an interposer (which means a substrate mounted to the other substrate), the electronic apparatus is preferably structured such that the high heat conducting member is arranged so that the other substrate to which the interposer is mounted and the high heat generation electronic part are in contact with each other via the high heat conducting member, or such that the high heat conducting member is arranged so that the other substrate to which the interposer is mounted and a metal plate constituting the substrate used as the interposer are in contact with each other via the high heat conducting member.
In this case, when using an iron series alloy containing at least any one of nickel, chrome, cobalt and aluminum, an iron series composite material obtained by applying a copper clad to the iron series alloy, tungsten, copper, molybdenum, tantalum, nickel, aluminum or the like, for the metal plate mentioned above, it is possible to provide with a high heat conducting property and a high rigidity. For example, as shown in Table 1, when using the copper or the aluminum, not only it is possible to manufacture inexpensively, but also the heat conductivity is high, so that an improved heat radiation can be achieved. Further, in the case that the main substrate is set to a substrate employing a ceramic such as an alumina, a glass ceramic or the like, since an inbar (iron-36 wt % nickel alloy) or 42 alloy (iron-42 wt % nickel alloy) has a high elasticity and a low coefficient of thermal expansion, it is possible to make a difference of thermal expansion coefficient between the interposer and the main substrate small by using a metal core interposer employing them, and it is possible to improve a solder connection reliability. In particular, an alloy having iron-nickel as a main component such as the inbar or the 42 alloy can be made an interposer having a coefficient of thermal expansion in correspondence to the kind of the main substrate, by changing a composition thereof, and it is possible to improve the solder connection reliability between the main substrate and the interposer.
Further, in the case of using the high elastic metal having the iron-nickel as the main component mentioned above as the metal plate mentioned above, since they have a low coefficient of thermal conductivity, it is preferable that the structure is made such that a surface thereof is coated with a member having a high coefficient of thermal conductivity, for example, a copper plating (composite metal plate). This coating can be also effectively used at a time of executing a roughening process for improving an adhesion to an insulating resin.
In this case, the member having the high thermal conductivity mentioned above means a material having a high coefficient of thermal conductivity in comparison with a resin material such as an epoxy polyimide or the like (coefficient of thermal conductivity: 0.2 to 0.3 W/m.k), which are generally used as an insulating material of the wiring substrate, and it is preferable to employ at least one of Al, silver, gold, conductive resin, copper and solder or a material (coefficient of thermal conductivity: some W/m.k or more) obtained by combining them.
In particular, in the case of employing at least the solder for the connection, since it is possible to form by using a mounting step (reflow) of the electronic part, it is possible to simplify a process step.
Further, taking the mounting to the electronic part, it is desirable to form the metal (particularly, Al, silver or gold) electrode in the electronic part and make a structure so as to connect the electrode to the metal plate by the solder, the conductive resin or the like. In some cases, in order to achieve a low cost, it is possible to connect an electronic part which is not provided with a metal electrode only particularly used for connection, by a conductive resin such as a silver paste or the like, or an adhesive agent. In this case, the adhesive agent is not advantageous in view of a heat radiation.
Further, the conducive layer mentioned above may employ a foil made of stainless, nichrome, tungsten, aluminum or the like which is generally used in a multi-layer wiring substrate, however, is preferably a copper foil.
Further, as a method of forming a via hole for heat radiation, a drilling, a plasma application or a photolithography of a resin in which a photosensitive material is mixed may be employed, however, a process in accordance with a laser beam is desirable. It is possible to form by using a CO2 laser, an ultraviolet laser, an Xe laser, an excimer laser, a YAG laser, a YLF laser, an Ar laser or the like having a high energy output, as the laser, however, it is preferable to form by the CO2 laser or the ultraviolet laser. In particular, since the ultraviolet laser has a characteristic of resolving the resin without carbonizing so as to form a via hole having a fine diameter, it is possible to prevent an unnecessary contact between the member having the high thermal conductivity and the signal wiring. Further, when using the drilling, it is possible to reduce a manufacturing cost.
It is preferable to use any of copper, tin, solder, nickel, chrome, gold and composite material thereof, for plating of the wire forming method employed in the present invention.
A method of connecting the electronic part and the metal plate in the substrate via the via hole for heat radiation employed in the present invention includes a method of connecting in accordance with a metal plating, a method of applying and charging a conductive material (a resin, an adhesive agent, a conductive resin or the like obtained by mixing a metal filler) to the via hole, a method of charging the solder and the like.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.